Sensory systems are the means by which people receive the information they need to navigate about the world. Of all of the major modalities olfaction is perhaps the least understood, despite the fact that it plays many important roles in our lives. The work described in the present proposal is designed to examine carefully a very important region in the central olfactory pathways. The anterior olfactory nucleus (AON) has synaptic connections at nearly every point of information processing on both the ipsilateral and contralateral side of the olfactory regions of the forebrain. As such, it is capable of driving or modulating the synaptic activity of the entire central olfactory system. Nevertheless, it has been virtually ignored compared with studies of the olfactory mucosa, bulb and piriform cortex. The proposed research will continue our examination of the AON's structure and function. The work has two major foci. First, while the region may have one name, it is becoming obvious that it contains several different processing areas and is therefore more complicated than initially believed. The primary goal of this research is to define functional subregions in the AON to build fundamental information about its organization. Second, the existence of crossed connections in the olfactory system has received very little attention. In nearly every sensory, motor and neocortical system crossed connections are important in facilitating complex information processing and the work examining them has led to enormous advances in understanding system function. Understanding the contributions of interhemispheric connections in the olfactory system will doubtlessly also lead to more a sophisticated view of the mechanisms of odor perception.